[R] how to put the results of loop into a dataframe

Philipp Pagel philipp.pagel.lists at t-online.de
Tue Jun 20 10:24:08 CEST 2006

On Tue, Jun 20, 2006 at 09:09:16AM +0800, zhijie zhang wrote:
>  suppose i want to do the following caulation for 100 times, how to put the
> results of x , y and z into the same dataframe/dataset?
> x<-runif(1)
> y<-x+1
> z<-x+y

Several possibilities:

1) Use rbind

Before loop:

d = NULL

And in the loop:

d = rbind(d, data.frame(x, y, z))

2) Build empty data frame of desired size beforehand and fill by row

E.g. for 10 rows:
d = data.frame( x=rep(0, 10), y=rep(0,10), z=rep(0,10))

And in the loop (index i):

d[i, ] = c(x, y, z)

3) Build vectors first, dataframe after the loop

x = NULL
y = NULL
z = NULL

in the loop:

x = append(x, runif(1))

After loop:

d = data.frame(x, y, z)

Solutions 1&3 are slower but you don't need to know the final number of
rows in advance. Solution 2 is cleaner, in my opinion, but requires that
you know the final size.

Of course, for the particular example calculation you don't need a loop
at all:

x = runif(100)
y = x+1
z = x+y
d = data.frame(x,y,z)


Dr. Philipp Pagel                            Tel.  +49-8161-71 2131
Dept. of Genome Oriented Bioinformatics      Fax.  +49-8161-71 2186
Technical University of Munich
Science Center Weihenstephan
85350 Freising, Germany


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